Injection valve timing sensor

Abstract

A fuel injector has a lift sensor in the form of a cylindrical piezoelectric ceramic member having metal film electrodes on each side thereof and which is sandwiched between an insulated terminal element having a flat surface abutting one side of the piezoelectric element and a flat ground plate formed with projections which projections engage the wall of a bore in which the piezoelectric element is disposed so as to both hold the element in place and establish an electrical connection between the housing in which the bore is formed and the second side of the piezoelectric element. A spacing shim having a flat surface abutting the ground plate engages one end of a spring which biases the valve element of the fuel injector toward a closed position.

What is claimed is: 
     
       1. In a fuel injector of the type having: a housing;   a nozzle disposed in said housing;   a valve element operatively disposed in said nozzle for controlling an injection orifice thereof;   a spring engaging said valve element at one end thereof for biasing said valve element toward a position in which said valve element closes said injection orifice;   a piezoelectric element disposed in said housing;   a lift sensor comprising:   a terminal element disposed in contact with a first side of said piezoelectric element, said terminal element being insulated from said housing and projecting out of said housing through an opening formed therein; and   means interposed between said spring and a second side of said piezoelectric element for establishing electric contact between said second side of said piezoelectric element and said housing and for retaining said piezoelectric element within said housing, said means being defined by a ground plate having the form of a metallic disc having a plurality of projections extending from the periphery thereof, said projections engaging a wall of said housing to establish said electrical contact and to hold said piezoelectric element within said housing, said ground plate having a surface area nearly equal to or greater than that of said second side.   
     
     
       2. The apparatus as claimed in claim 1, wherein said terminal element is formed with a flat surface, said flat surface being adapted to abut said first side of said piezoelectric element so as to uniformly apply force thereto. 
     
     
       3. The apparatus as claimed in claim 1, further comprising a spacing shim interposed between said ground plate and said spring, said shim having a flat surface in contact with said ground plate so as to uniformly apply force to said second side of said piezoelectric element via said ground plate. 
     
     
       4. The apparatus as claimed in claim 1, wherein said terminal element takes the form of a terminal pole disposed through an insulating body and a disc connected to one end of said pole. 
     
     
       5. The apparatus as claimed in claim 1, wherein said piezoelectric element has button-like cylindrical configuration and is formed with first and second metal film electrodes on said first and second sides, respectively, said first and second electrodes being formed to terminate short of the peripheral edge of said piezoelectric element. 
     
     
       6. In a fuel injector of the type having: a housing;   a nozzle disposed in said housing;   a valve element operatively disposed in said nozzle for controlling an injection orifice thereof;   a spring engaging said valve element at one end thereof for biasing said valve element toward a position in which said valve element closes said injection orifice;   a lift sensor comprising:   a piezoelectric element disposed in said housing, said piezoelectric element having a cylindrical configuration and being formed with first and second metal film electrodes on said first and second sides respectively, said first and second electrodes being formed to substantially cover said first and second sides and terminate short of the peripheral edge of said cylindrical piezoelectric element for preventing electrical discharges between said first and second electrodes and said housing;   a terminal element disposed in contact with said first electrode of said piezoelectric element, said terminal element being insulated from said housing and projecting out of said housing through an opening formed therein;   means defining a first flat surface on that portion of said terminal element in contact with said first electrode, said flat surface having a surface area nearly equal to or greater than that of said first electrode for applying a uniform force to said piezoelectric element;   a dis-shaped ground plate interposed between said spring and the second side of said piezoelectric element, said ground plate establishing electric contact between said second electrode of said piezoelectric element and said housing, and engaging said housing for retaining said piezoelectric element within said housing; and   means defining a second flat surface on that portion of said ground plate in contact with said second electrode, said second flat surface having a surface area nearly equal to or greater than that of said second electrode for applying a uniform force to said piezoelectric element.